Variable valve control comprising a sliding-block part and a free travel

ABSTRACT

The invention relates to a variable valve train for reciprocating engines, in particular internal combustion engines comprising at least one cam of a camshaft that is rotatably mounted in the cylinder head. Said cam actuates a lift valve using a pulley assembly which can be displaceably guided in a sliding-block part along an adjusting inclined plane, together with a valve actuating element which is connected in series. The valve stroke can be adjusted in a variable manner in relation to the cam by the displacement of the sliding-block part and the pulley assembly is elastically pre-tensioned in relation to the cam. To achieve a sturdy valve train which exhibits uniform valve accelerations, a free travel (s) that allows an excitation movement of the pulley assembly is provided between the cam heel and the valve actuating element. The valve actuating element is configured as a two-part cam follower with a rocker action and the sliding-block part has a sliding-block guide comprising an additional excitation inclined plane for the pulley assembly.

[0001] The invention relates to a variable valve control device for reciprocating engines, internal combustion engines in particular, as specified in the preamble of Claim 1.

[0002] Such a variable valve control device is disclosed, for example, in DE 42 23 173 A1; it is a device in which an adjustable sliding block (rocker arm) element in the cylinder head of the internal combustion engine, with an inclined adjusting plane and a roller, is introduced between the cam of a camshaft on one side and the cup stem on the shaft end of an upper valve on the other side. Both a full stroke and partial strokes to around zero stroke can be controlled by displacement of the sliding block element relative to the cam. In the case of a full stroke such displacement results in valve actuation which with respect to valve lift and velocity profile development is determined by the geometry of the cam and the inclined adjusting plane and which may be correspondingly optimized. In the case of the partial stroke, of course, first an idle stroke (=excitation movement) is executed and then the partial stroke (=generation movement), a cam area exerting its effect later in time in this instance, an area which of necessity may cause a different velocity profile development or high, jerky valve accelerations. This applies both to valve opening (upward slope) and valve closing (downward slope).

[0003] The object of the invention is to create a generic variable valve control device which permits extensive valve stroke changes accompanied by valve actuation as free of jerkiness as possible and which is of rugged design and cost-effective in manufacture.

[0004] It is claimed for the invention that this object is attained by the features specified in Claim 1. Advantageous developments of the invention are specified in the additional claims.

[0005] It is proposed in accordance with the invention that there be inserted between the cam and the valve actuation element, a valve rocker in particular, an empty run (free travel) component which effects preacceleration (excitation movement) of the sliding block in the case both of a full stroke and partial strokes of the upper valve, so that the generation movement (opening movement) of the upper valve is controlled with the positive and negative acceleration desired essentially by the inclined adjusting plane of the rocker arm element. This decoupling of excitation movement and generation movement executed by the geometric design of cam and variable valve control device creates a velocity profile without higher acceleration peaks and accordingly a rugged valve train which is improved from the viewpoint of wear and operating noise, to the greatest extent possible independently of the assigned valve travel.

[0006] The layout of the valve train as specified in Claim 3 additionally permits longer valve strokes and accordingly a larger valve stroke adjustment range determined by a valve rocker having the associated more favorable rocker ratios and by the positioning of the inclined adjusting plane more or less perpendicular to the axis of rotation of the cam, which results in shorter lateral travel distances of the roll pack especially during excitation movement. In this situation the contact surface of the valve rocker for the roll pack may be oriented parallel to the direction of displacement of the rocker arm element.

[0007] In another advantageous embodiment of the invention the inclined adjusting plane of the rocker arm element is in the form of a slotted rocker arm guide whose opposite guide surface forms an inclined preacceleration plane in excitation movement of the sliding block element which provides smooth transition to the inclined contact plane section of the inclined adjusting plane for the movement of generation. This results in gentle sliding positioning of the sliding block element on the valve rocker followed by generation movement without a transitional element.

[0008] The sliding block element may advantageously be pretensioned against the cam by means of at least one simple spring clip. The spring clip may preferably be supported on the rocker arm element by one of its sides and acts in conjunction with a second, elongated side on the sliding block element pretensioning the latter against the cam.

[0009] In the case of use of a hydraulic valve play equalization element in the valve train in particular it may be advantageous for the valve rocker to rest against a stop of the rocker arm component when the upper valve is in the closed position. The pulley assembly may be lifted by the valve rocker as a result of pretensioning of the spring clip, so that constant contact is established between the sliding block element and the cam, and free play is established between the valve rocker, the rocker arm element, and the valve shaft.

[0010] In order to achieve a valve rocker structure which is rigid and produces high layout accuracy, preference is given to mounting the valve rocker in the cylinder head by way of one valve rocker axis. In this situation the hydraulic valve play equalization element could then be mounted on the end of the valve rocker operating in conjunction with the shaft end of the upper valve. It is proposed, however, that preference be given to a valve rocker in at least two parts, one part of which is pivotably mounted, while the other part resembling a rocker rests on one side on the hydraulic valve play equalization element and on the other on the shaft end of the upper valve, the two interposed valve rocker parts being connected to each other in operation (by means of a carrier extending transversely or by a pin joint connection).

[0011] One exemplary embodiment of the invention is explained in greater detail in what follows. The drawing illustrates

[0012] in FIG. 1 a cross-section through a variable valve train in the cylinder head of a reciprocating internal combustion engine along line I-I of FIG. 2, with a cam, a movable rocker arm element, a sliding block element, and a valve rocker acting on an upper valve;

[0013] in FIG. 2 a view of the valve train along arrow X in FIG. 1;

[0014] in FIG. 3 a side view of the two-part valve rocker mounted between the rocker arm element and the upper valve;

[0015] in FIG. 4 a top view of the valve rocker shown in FIG. 3;

[0016] in FIG. 5 diagrams of the valve train in the case of a full stroke; and

[0017] in FIG. 6 the same diagrams for a partial stroke of the upper valve.

[0018] In FIGS. 1 and 2, 10 designates a camshaft which is rotatably mounted in a cylinder head 12 (only part of which is shown) of a multiple-cylinder reciprocating internal combustion engine and which carries a cam 14 for actuation of intake upper valves, only one upper valve or its vertical shaft 16 being shown.

[0019] In order to obtain a variable valve train, a rocker arm component 18 is movably mounted by way of fitting bores (20) in the cylinder head 12 on stationary guide pins 22. The rocker arm component 18, may be adjusted in the direction of the double arrow 24 by means of an adjusting mechanism not shown (such as an eccentric shaft adjusted by hydraulic or electric means).

[0020] The more or less U-shaped rocker arm component 18 with a base wall 56 has in each of the lateral legs 26,28 a rocker arm guide with an inclined adjusting plane 30 and an inclined preacceleration plane 32.

[0021] A sliding block element 34 is inserted so as to be movable into the slotted rocker arm guide 30,32 open at the top. The sliding block element 34 has a central roller 34 a (FIG. 2) which rolls on the cam 14. To the left and right of this element 34 two other rollers 34 b,34 c are provided which roll on the contact surfaces 36 a,36 b of a valve rocker 36, the rollers in question being mounted on roller bearings on a transfer pin 34 d which operates in conjunction with the inclined planes 30,32 in question.

[0022] The valve rocker 36 is made up of a first H-shaped valve rocker component 40 and an interposed valve rocker component 42 which are mounted as follows.

[0023] The first valve rocker component 40 is one side mounted by way of mounting bores 44 on stationary valve rocker shafts 46 and carries the contact surfaces 36 a,36 b for the rollers 34 b,34 c of the sliding block element 34. In addition, the valve rocker component 40 has a carrier 48 extending transversely which acts on the interposed second valve rocker component 42 as a counterpoise.

[0024] The second valve rocker component 42 rests on one side, by way of a ball socket 50, on a valve play equalization element 52 having a corresponding ball end which is mounted in the cylinder head 12 as illustrated. The other end of the component 42 has mounted on it a carrier 53 which operates in conjunction with the end of the shaft of the upper valve 16.

[0025] The layout described creates precise valve operation with the valve play equalization element 52 at rest (lower weights in motion).

[0026] As is to be seen from FIG. 1 in particular, the inclined adjusting plane 30 viewed as a whole is positioned more or less perpendicular to the direction of adjustment 24 of rocker arm component 18 and the sliding block element 34 acts on the valve rocker 36, its contact surfaces 36 a,36 b being oriented parallel to the direction of adjustment 24. The valve rocker 36 is situated more or less beneath the camshaft axis of rotation 10 a between the rocker arm component 18, which is adjustable tangentially to the cam 14 and the upper valve 16.

[0027] The valve rocker 36 (see FIGS. 3 and 4) or its valve rocker component 40 is positioned, in the situation illustrated in FIGS. 1 and 2 (corresponding to a full stroke), with the upper valve 16 closed, on a stop 54 of the base wall 56 of the rocker arm component 18, the valve rocker 36 being kept free of play by way of the valve play equalization element 52.

[0028] In this position the sliding block element 34 has a no-load run s as viewed between the contact surfaces 36 a,36 b of the valve rocker 36 and the base circle 14 b of the cam 14.

[0029] This no-load run s results in lifting of the sliding block element 34 from the contact surfaces 36 a,36 b of the valve rocker 36, since two clip springs 56 fastened in the rocker arm component 18 pretension the sliding block element 34 under spring tension against the cam 14 by one of their clips 56 a. As is to be seen from FIG. 2, the clips 56 a engage the transfer pin 34 d between central roller 34 a and the two adjacent rollers 34 b,34 c, while their second spring 56 b rests on the rocker arm component 18.

[0030] The sliding block element 34 is thereby preaccelerated first in excitation movement in the area of the no-load run s, this no-load run increasing in proportion as the valve stroke (displacement of the rocker arm component 18 in FIG. 1 of the drawing to the right) decreases.

[0031] This excitation movement of the sliding block element 34 increases as a result of the shape of the inclined preacceleration plane 30 until the transfer pin 34 d is shifted onto inclined starting plane section 30 a of the inclined adjusting plane 30, this pin 34 d simultaneously running up by way of the rollers 34 b,34 c on the starting surfaces 36 a,36 b of the valve rocker 36 and actuating the upper valve 16 in further generation movement. Section 30 a extends more or less tangentially to the cam 14 or its inclined starting and ending plane.

[0032] On the other hand, when the upper valve 16 closes, the valve rocker 36 ultimately reaches the stop 54 and then lifts the sliding block element 34 from the valve rocker 36, within the limits of the no-load run s present precisely at this time.

[0033] The geometric configuration of the cam 14 and the inclined adjusting-planes 30,32 in the rocker arm component 18 are discussed in detail with reference to the diagrams in FIGS. 5 and 6.

[0034]FIG. 5 illustrates the movement curves for a full stroke and FIG. 6 the movement curves for a partial stroke of the upper valve 16. The vertical lines designate the respective valve stroke s_(v).

[0035] Curve a corresponds to the movement of adjustment of the sliding block element 34, the parts of the excitation movement corresponding to the no-load run s of the sliding block element 34. It is to be considered to be essential to this invention that even in the case of a full stroke (FIG. 5) a no-load run s is present which places the starting point of the movement of generation (valve actuation) on the branch between b and c of curve a which corresponds in approximation to uniform valve acceleration.

[0036] Curve d describes the geometric configuration of the inclined adjusting plane 30, which in conjunction with the configuration of curve a yields the actual valve lift by way of valve stroke s_(v) illustrated by curve e. Additional curve f describes the course of valve acceleration, it being noteworthy that the acceleration peaks are more or less the same in full stroke (FIG. 5) and partial stroke (FIG. 6).

[0037] Consequently, the valve train described makes possible “full” valve lift curves e for the full stroke of upper valves 16 without elevated acceleration peaks in the case of a partial stroke. 

1. A variable valve train for reciprocating engines, internal combustion engines in particular, with at least one cam of a camshaft rotatably mounted in a cylinder head, which cam actuates an upper valve by way of a sliding block element movably guided in a rocker arm component along an inclined adjusting plane and a valve actuation element mounted downstream in the process, the valve stroke being variably adjustable relative to the cam by displacement of the rocker arm component and the sliding block element being pretensioned against the cam by a spring, characterized in that a no-load run (s) permitting excitation movement of the sliding block element (34) is provided between the cam base circle (14 b) and the valve actuating element (36).
 2. The valve train as specified in claim 1, wherein the excitation movement of the sliding block element (34) corresponds to the initial acceleration and final deceleration of the profile of the cam (14, FIG. 5, curve a, no-load run s).
 3. The valve train as specified in claim 1 or 2, wherein the inclined adjusting plane (30) as a whole is oriented so as to be more or less perpendicular to the adjustment movement (double arrow 24) of the rocker arm component (18) and wherein the sliding block element (34) acts on a valve rocker (36) mounted on one side so as to be movable, a valve rocker (36) which is mounted more or less beneath the camshaft rotation axis (10 a) between the rocker arm component (18) adjustable tangentially to the cam (14) and the shaft end of the upper valve (16).
 4. The valve train as specified in claims 1 to 3, wherein the inclined adjusting plane (30) has an inclined starting ramp section (30 a) extending nearly tangentially to the cam (14).
 5. The valve train as specified in claims 3 and 4, wherein the starting surfaces (36 a,36 b) of the valve rocker (16) for the sliding block element (34) are oriented parallel to the direction of displacement (24) of the rocker arm component (18).
 6. The valve train as specified in one or more of claims 1 to 5, wherein the inclined adjusting plane (30) is formed in a slotted rocker arm guide the opposite guide surface of which forms an inclined preacceleration plane (32) for the excitation movement (no-load run s) of the sliding block element (34).
 7. The valve train as specified in one or more of claims 1 to 6, wherein the sliding block element (34) is pretensioned by means of at least one spring clip (56) against the cam (14).
 8. The valve train as specified in claim 7, wherein at least one spring clip (56) is held directly on the rocker arm component (18) by one of its sides (56).
 9. The valve train as specified in one or more of claims 1 to 8, wherein the valve rocker (36) rests against a stop (54) of the rocker arm component (18) when the upper valve (16) is in the closed position.
 10. The valve train as specified in one of claims 1 to 9, wherein the rocker arm component (18) is guided by way of suitable fitting bores (20) on guide pins (22) fastened on the cylinder head (12).
 11. The valve train as specified in one or more of claims 1 to 10, wherein the valve rocker (36) is pivotably mounted by way of one or more valve rocker shafts (46).
 12. The valve train as specified in claim 1, wherein the valve rocker (36) is in at least two parts, the first valve rocker component (40) being pivotably mounted over the valve rocker shafts (46) and having the contact surfaces (36 a) for the sliding block element (34) and operating from the viewpoint of drive in conjunction with a second valve rocker component (42) mounted in parallel with the first valve rocker component (40) and being pivotably mounted on one side on a hydraulic valve play equalization element (52) and on the other side engaging the shaft end of the upper valve (16).
 13. The valve train as specified in claim 12, wherein the first valve rocker component (40) is in the form of an H, with two valve rocker sections with contact surfaces (36 a) and a carrier (48) extending transversely and acting on the second valve rocker component (42), and wherein the second valve rocker component (42) extends between the two rocker sections of the first valve rocker component (40). 